Field of the Invention
The present invention relates to a current measurement method and current measurement device for detecting a magnetic field near a primary conductor to which a measurement target current flows, thereby obtaining the amount of the measurement target current.
Description of the Related Art
For current measurement, there has conventionally been proposed a current sensor that causes a sensitive magnetic detection element to detect a revolving magnetic field by a measurement target current near a primary conductor to which the measurement target current is applied.
For example, Japanese Patent Laid-Open No. 2001-264361 discloses a compact current sensor configured to cause one sensitive magnetic detection element (MI element) to detect a revolving magnetic field by a current flowing to a primary conductor.
In this arrangement, if the electric wire to which the measurement target current flows is isolated, no problem arises. However, if currents of adjacent phases flow in parallel, as in, for example, a three-phase power supply, magnetic fields by the adjacent currents are superimposed, and the measurement accuracy degrades.
To avoid this influence, generally, a magnetic shield is generally provided by surrounding the magnetic detection element with a magnetic material such as Permalloy. However, the magnetic shield may form a magnetic circuit and distort a magnetic field from a current, and it is difficult to completely cope with the problem.